How-To: Identifying Aster Yellows

I first saw aster yellows last year on a solitary coneflower bloom. The odd growth pattern of the bloom had me mesmerized, delighted and a little stumped. Was this bloom that looked like fireworks a good find, or a sign of something terrible? Turns out it was not good, not good at all.

Aster yellows is a plant disease caused by the aster yellows phytoplasma, a bacterium-like organism that lives in the food-conducting tissue (phloem) of plants. The disease affects 300 species in 38 families of broad-leaf herbaceous plants, primarily in the aster family, as well as important cereal crops. Entire stands of plants can be affected. The disease occurs across North America.

Transmission of the Disease The disease is transmitted by the aster leafhopper, Macrosteles quadrilineatus. When a leafhopper inserts its stylet into the plant to feed on the phloem of an aster yellows infected plant, it acquires the phytoplasma. The phytoplasma goes through an incubation period during which it multiplies within the leafhopper and then moves to the salivary glands. The leafhopper then transmits the phytoplasma via its saliva when it feeds on a new plant. The newly transferred phytoplasma is deposited into a healthy plant, and within 8 to 12 hours the phytoplasma moves into the host plant’s phloem.